Corn-Friendly Fungus Tapped
for Service

Microbiologist Don Wicklow examines
a culture of Acremonium zeae.
Cultures of A. zeae isolates
from corn can be seen on the
computer screen. (D002-1)

Acremonium zeae is a type of fungus called an endophyte that
lives inside the kernels of corn plants, neither harming nor benefiting
its host.

Or so scientists thought.

Now, Agricultural Research Service
(ARS) and University of Iowa (UI) scientists have found that corn plants
do indeed benefit from the endophyte's presenceespecially as they
try to ward off other fungi, like Aspergillus flavus and Fusarium
verticillioides. Both are species of toxin-producing molds that
can cause multimillion-dollar losses to the U.S. corn crop.

In studies at ARS's National Center for Agricultural Utilization Research
in Peoria, Illinois, and UI's Department of Chemistry in Iowa City,
collaborating scientists Don Wicklow and Jim Gloer showed, for the first
time, that the endophyte secretes an antifungal concoction that may
stop the molds from growing inside the seed.

"Acremonium zeae is mostly a benign player in corn, but
it produces compounds called pyrrocidines that work against the Aspergillus
and Fusarium fungi as well as some bacteria," says Wicklow,
a microbiologist in the ARS center's Mycotoxin Research Unit. "Pyrrocidines
are the first natural products reported from this common fungal endophyte
in corn."

Lab tests by Wicklow's group showed that the endophyte is antagonistic
to the molds and interferes with Aspergillus's ability to infect
ripening corn kernels and contaminate them with a carcinogen called
aflatoxin. Such antagonism may also protect the corn plant from the
F. verticillioides disease, stalk rot. Gloer's lab studied the
antifungal activity of extracts from A. zeae lab cultures and
identified the source as two recently reported antibiotics, pyrrocidines
A and B.

In 2002, Wicklow followed up that work by inoculating field plots of
corn with the endophyte. He demonstrated that A. zeae can naturally
produce the pyrrocidines in corn and that the treatment could slow spread
of Aspergillus in the crop's seed.

"This was important to nail down," Wicklow says, "because
then we would have documentation that the compounds are also produced
naturally in corn kernels, where interference with A. flavus
or F. verticillioides infection would occur."

Initially, they found pyrrocidines as major components in culture extracts
of just 2 of 13 A. zeae isolates obtained from the ARS Culture
Collection, housed at the Peoria center. But a later switch to liquid
chromatography and mass spectrometry detection methods revealed that
12 of the 13 isolates produced the pyrrocidines.

The discovery warrants a closer look at A. zeae's importance
in corn, Wicklow notes, but the practical implications remain to be
seen. "You can't simply pump these pyrrocidines into corn,"
he notes. "But A. zeae is carried naturally within the seed,
growing into the seedling and spreading throughout the plant. We can
study the environmental conditions under which it becomes the dominant
fungus in corn and look there for clues to controlling Aspergillus
and Fusarium."By Jan
Suszkiw, Agricultural Research Service Information Staff.

This research is part of Plant Diseases, an ARS National Program
(#303) described on the World Wide Web at www.nps.ars.usda.gov.